Photo: NASA E/PO, Sonoma State University, Aurore Simonnet
This week I attended The Secret Science Club to hear Caleb Scharf, the director of the Astrobiology centre at Columbia University, talk about black holes.I discovered some mind-blowing facts about black holes that I didn’t know: I used to think they were just these mysterious destructive forces in the universe that vacuumed up matter.
While this is partly true, black holes are also very dynamic. They spit out huge energy beams, shaping the universe around them, and may have been necessary for creating life on Earth.
I always attributed the discovery of black holes to Einstein.
While Einstein did revive the theory in 1916, John Mitchell actually thought of it first, back in 1783. The idea didn't go anywhere, though, because he didn't know what to do with it.
Mitchell started to develop the theory of black holes when he accepted Newton's theory that light consists of small material particles, called photons. He wondered how the movement of these light particles is impacted by the gravitational pull of the star they are escaping, and what would happen to these particles if the gravitational pull was so strong that light could not escape.
Mitchell is also the founder of modern seismology, when he suggested earthquakes spread out as waves through the earth.
Last night Scharf said to think of space as a rubber sheet. Think of the mass of a planet as a ball pushing down on the rubber sheet. The sheet of space becomes distorted and no longer has straight lines. This creates a gravitational pull, and explains why planets orbit the sun.
Space can become increasingly distorted as an object's mass gets larger. This further distortion increases gravity and accelerates orbits, pulling anything around the object in faster and faster.
For example, the orbit of mercury around the sun is 30 miles per second, but the orbit of the stars close to the black hole at the centre of our galaxy is 3,000 miles per second.
If this pull is strong enough, the orbiting object gets pulled into the larger object.
We usually think of a black hole as just one kind, but astronomers have recently noticed that they come in different variations.
There are spinning black holes, electrical black holes, and black holes that do both. Regular black holes grow by swallowing matter, and spinning black holes are formed by the merging of two of them.
These black holes put out even more energy, because of their increased distortion of space. They make it impossible for matter near them to stand still or orbit slowly. A charged, spinning black hole can act as a particle accelerator.
One black hole called GRS 1915+105, about 35,000 light-years from Earth, is spinning more than 950 times per second.
Black holes have to hold a massive amount of mass in an incredibly small space to have the required gravity to pull light in. For example, to make a black hole with the mass of Earth, the entire planet would need to be squeezed down to a space 9 millimeters across.
A black hole with 4 million times the mass of our sun can fit into the space between Mercury and the Sun. Black holes in the centre of galaxies could have a mass of 10 to 30 billion times the mass of our sun.
Having such a large mass in a tiny area means the black hole is incredibly dense, and the forces inside the black hole are incredibly strong.
As everything around the black hole is pulled into its gaping maw, all of this stuff speeds up. The event horizon supercharges the speed of particles close to the speed of light.
Scharf said that when stuff falls through the centre of the event horizon there is a gurgling sound. This sound is the energy of motion being converted into sound waves. He described the noise as the sound you hear when water is released from a bath.
In 2003 astronomers using NASA's Chandra X-ray observatory, detected sound waves coming from a supermassive black hole 250 million light years away.
When anything (be it planets, suns, galaxies or particles of light) passes close to a black hole, they will be pulled in by its gravity. If something else acting on the object, like say a rocket, is stronger than the black hole's gravity, it can escape the pull.
Until, of course, it reaches the event horizon: The point where escape from a black hole is impossible. In order to escape the event horizon, objects must move faster than the speed of light, which is impossible.
This is the 'black' part of the black hole, because if light can't escape, then we can't see inside and the area looks empty.
Researchers think that even small black holes would tear you apart before you fall through the event horizon. Gravity is stronger the closer you get to a planet, star, or black hole. If you were falling feet first, gravity at your feet would be so much stronger than at your head. This force would pull you apart.
Light bends around the event horizon and eventually gets pulled into nothingness as it falls through.
Scharf describes what we would see if a clock were to be sucked into a black in an interview with The Economist. He says the ticking of the clock (if it were to survive the forces of the black hole) would appear to slow down as it approached the event horizon and eventually would seem to freeze altogether.
This freeze in time is due to gravitational time dilation, explained by Einstein's theory of relativity. The gravity of a black hole is so strong, it can slow down time. From the clock's perspective it is still functioning normally. The clock would fade from view as the light from it is stretched further apart. The light would become increasingly red as the wavelength becomes longer and falls out of the visible light spectrum, vanishing from sight.
Black holes vacuum up the mass surrounding them, and in the black hole this mass gets squished together so hard that space between the individual components of the atoms is compressed, and it is broken down into subatomic particles that can stream away.
These particles are released in jets, as seen in this picture taken with NASA's Chandra X-ray Observatory. These particles propel out of the black hole due to intense magnetic field lines that can cross the event horizon.
Breaking up the particles creates energy, in an efficient manner. Converting mass into energy in this way is 50 times more efficient than nuclear fusion.
Some researchers think that black holes help create the elements because they break down matter into subatomic particles.
These particles can be used to create stars which in turn create elements heavier than helium, like iron and carbon, essential to the formation of rocky planets and life.These elements are what all mass is made of, including us.
Scharf tells The Economist, 'Take away the black holes and you get a different mix of elements, in different places. You might also get different, more volatile stars, which explode in a destructive supernova, blowing away inchoate complex structures.' Life may not have been possible without black holes.
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